Telephone networks are generally designed to support voice-band communication. The voice-band is the range of frequencies that is generally audible and is used for the transmission of speech. The voice-band ranges from approximately 300 Hz to 4000 kHz.
FIG. 1 shows telephone network 100. Central Offices (COs) 110 connect to individual subscribers through a main distribution frame (MDF) 130. A twisted pair of copper wires 140 typically connects an MDF 130 to a subscriber 150. The copper wire connection between MDF 130 and subscriber 150 is called a local loop (or a telephone loop). Local loops are generally designed for voice-band communication.
Broadband technology uses frequencies that are much higher than the voice-band. Digital subscriber line (DSL) technology, for example, uses frequencies that typically range from approximately 25 kHz. to approximately 1.1 MHz. Because local loops are designed for the voice-band, not all local loops will support broadband services. In a typical telephone network, some local loops will support broadband services and some local loops will not support broadband services. Often, a telephone company does not know which local loops will support broadband services.
Typically, broadband service providers must determine which local loops are capable of supporting broadband services. It is expensive and labor intensive for service providers to send a technician to the home of an individual subscriber to test the subscriber's local loop. The process of qualifying local loops can be made much less expensive if a subscriber can be provided with the means to test her local loop.
A conventional means for testing whether a local loop can support broadband services employs information sequences exchanged between voice-band modems. During modem handshaking and training procedures, voice-band modems use voice-band signals to probe a local loop. These modems exchange information with each other through signals called information sequences. The information sequences contain a summary description of the channel capacity of the loop at various voice bands along with certain characteristics of the connection that was derived by the modems during handshaking and training. Estimations about the capacity of a local loop to support broadband services can be based on these information sequences.
Conventional loop testing methods do not access all of the information that modems derive during handshaking and training procedures. Also, conventional loop testing methods probe a local loop with test signals that have frequencies that are limited to the voice-band. Thus, conventional loop testing methods use test signals with a limited range of frequencies and do not employ all of the information generated by those test signals.